FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.
Article Id 231138

This article describes a solution when it is not possible to ping the hostname.

This article describes how to specify DHCP Domain Name (option code 15).

To set the DHCP option in the FortiGate interface, it will not be possible to set it through GUI.


Go Interface -> DHCP server -> Advance DHCP option, and select 'create new'.

It is necessary to configure it through CLI. It will show the warning message:

'This option may not function correctly. It should be set using the CLI attribute:domain'.




One more such error : 

When a DHCP option code 51 is added under ‘Additional DHCP Options’, it throws the following error:

‘This option may not function correctly. It should be set using the GUI field: Lease time.’






- The user can ping the whole FQDN but cannot ping the hostname.

- The user is using an Internal DNS server on FortiGate.

- The user is getting IP from the DHCP server on FortiGate.



It is necessary to configure the domain name via CLI:


# config system dhcp server

    edit <id>

        set domain <name>



For example, to configure it for the domain name 'meisystem.local'.


# config system dhcp server

    edit 4

        set domain “meisystem.local”



To verify if the domain is added or not:


# config system dhcp server

# show


Screenshot 2022-11-10 131327.png


Check by doing the following:

Run the following command on the user's machine:


- ipconfig / renew - To request new IP settings from the DHCP server.

- ipconfig /all.

- This will show DNS suffix which is configured as a domain name in the DHCP server.

- Now, it will be possible to ping hostname.


Solution for option code 51:


Option 51 refers to IP Address Lease Time.


A DHCP server uses this option to indicate the lease time it is prepared to give in a server reply (DHCPOFFER). The time is given as a 32-bit unsigned integer with seconds as the unit of measurement. This option's code is 51.


FortiGate provides an option ‘Lease time’ on GUI to assign the lease time under ‘DHCP Server’: